4
Introduction
ply in number and complexity, quickly becoming
mathematically intractable. To begin with, we
have the fundamental issue of power supply. A
mobile robot, just like fixed manipulators, should
be able of performing autonomously (i.e., without
external intervention) during long periods of time
operation; but these robots has to carry their own
power source on board, and any mobile platform
has restrictions regarding the maximum weight
of its payload. Closing the loop, power can only
be increased at the expense of larger and heavier
power supplies. This issue is analogous to the
one that limits the size and autonomy of space
ships—which led to the invention of multistage
rockets—or, for the matter, the one confronted by
all kinds of automobiles. It is not the only chicken
or the egg dilemma that we will find within mobile
robotics. If you have thought of the robot going
periodically and autonomously to a recharging
station (i.e., finding it, approaching it, using it),
please read the following issues.
A mobile robot must, by definition, change its
location in order to perform it tasks, which tears
down most of the other benefits enjoyed by ro-
botic manipulators. Free motion makes the current
environment of the robot vary, even largely, from
one moment to another. Occasionally, engineers
can build a model of the whole workspace, but in
most practical applications, it is common having
to face at least partially unknown regions. It is
difficult to plan any complex sequence of actions
with limited knowledge of their effects in all the
particular scenarios that the robot may encounter:
possibilities explode exponentially with time, and
thus planning must be stopped regularly to per-
ceive, analyze, and correct the results. Sensors
become crucial devices for mobile robots pre-
cisely for that reason. The process of transforming
sensory data into useful information, i.e., percep-
tion, arises then with all its complexity.
Motion also leads to the possibility of operating
in spaces that are potentially unlimited in size (that
is one of the main advantages of mobile robots,
after all!). The issues that can arise from this are
obvious for a programmable machine that has
finite memory and computational capabilities—
which, again, can only be increased at the expense
of more size and weight, feeding again the beast
of the power supply. Therefore, approximations
may have to be done even for problems otherwise
solvable. Furthermore, aside from computational
limitations, we find the issue of merging all the
information gathered at different locations of a
large environment in order to get a fairly complete
representation of it, which is a prerequisite for
planning future tasks.
Finally, the objects, people and other robots or
machines that a mobile robot is to interact with
during its performance can also be considered as
part of its environment, and as such they have a
relevant influence in not having a complete, static,
small model of the physical world. Unexpected
obstacles with arbitrary shapes and unknown
dynamics are one of the common problems that a
real mobile robot will have to face without much
previous knowledge. If those obstacles are intel-
ligent beings, understanding and predicting their
behavior becomes especially challenging.
In summary, the effects of including the capa-
bility of free motion in a robot lead to an important
increase in dimensionality, size, and complexity
of nearly all the issues of robotics at very different
levels, from mechanics to electronics to computer
science to artificial intelligence. Most of them
have no satisfactory solution yet—albeit many
proposals—, and that is the reason why today we
do not see mobile robots everywhere in the real
world, especially operating reliably during long
periods of time. It is also the reason why mobile
robotics remains such a fascinating discipline. It
will probably be for quite a while.
In spite of all these difficulties, there is one
basic problem of mobile robotics that has reached
a reasonable maturity in the last decades, up to the
point of being considered satisfactorily solved in
many practical situations. It has to do with mobile
robot navigation, that is, taking the robot from
one point to another. Maybe the reader who is